The lighting is brilliant in this picture as it is firmly focussed over the unicorns. You have kept all the colours in natural hues including the unicorns (where it can be tempting to add shades of neon and such) which keeps the picture together. I believe this is a photo manip, so the unicorns which have superimposed have been blended in really well. The direction of the light on the unicorns is the same as the background which is mainly why they blend so well. The unicorns point upwards leading the eye up and around the page. The unicorns themselves have been brilliantly rendered. The only query would be to somehow improve the shadow around the unicorns, but I know this is difficult and I can see you've taken a stab at doing it. Overall, carefully thought out and striking.